Preparation Of Ceria Micro/Nanostructured Materials And Their Properties

Nanostructured ceria (CeO2) has been attracting great interest because of the effective and the potential technological applications in catalysis. This paper focused on the fabrication of ceria nanostructured materials through hydrothermal method, including synthesis of CeO2 monodisperse nanoparticles, fabrication of monodisperse CeO2 hollow spheres constructed by nano-octahedra, and preparation of micro/nano CeO2 hollow spheres with mesoporous shells. Furthermore, the synthesis procedure, formation mechanism, and properties are also investigated. The detailed content of the dissertation is listed as follows:1. Controlled Synthesis of CeO2 Monodisperse NanoparticlesIn the first part, monodisperse CeO2 nanocubes have been fabricated via an acrylamide-assisted hydrothermal route. NH3 and acrylic acid from the hydrolysis of acrylamide act as OH-provider and capping reagent, respectively. On the basis of the experimental results, the formation of different morphologies could be ascribed to the initial valence state of cerium. When (NH4)2Ce(NO3)6 was used instead of Ce(NO3)3·6H2O, the resulting product was mainly uniform spherical particles. Moreover, KBrO3 was used as strong oxidizing agents to oxidize Ce3+to Ce4+. Thus CeO2 colloidal nanospheres with an average diameter of 60 nm have been fabricated. The structure and morphology of the samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), field-emission scanning electron microscopy (FE-SEM) and Fourier transformed infrared (FT-IR).2. Fabrication of Monodisperse CeO2 Hollow Spheres Constructed by Nano-octahedraMonodisperse CeO2 hollow spheres constructed by nano-octahedra have been synthesized by using CeCl3·7H2O as cerium source, and PVP, H2O2, and formamide as the reagent. A possible crystal growth and hollowing mechanism was suggested based on the detailed experiment. In addition, both the role of H2O2 and PVP in the formation of novel structured hollow spheres was investigated. The CO oxidation properties were investigated, and the novel structured CeO2 hollow spheres exhibited a higher catalytic properties compared to the commercial CeO2 powders.3. Preparation of Micro/Nano CeO2 Hollow Spheres with Mesoporous Shells.Based on the above successfully preparation of novel hollow spheres, we explore a new route of fabrication of micro/nano CeO2 hollow spheres with mesoporous shells, and the mesoporous hollow structures are of great interest owing to their high specific surface area and better permeation. The mesoporous CeO2 hollow spheres showed excellent adsorption capacity of organic pollutants (Congo red) from wastewater (about 84 mg Congo red/g). Furthermore, compared to commercial CeO2 powders, the prepared CeO2 hollow spheres exhibited a higher catalytic activity toward CO oxidation. Besides, CeO2 hollow microspheres with a mean diameter of 1.5 um and a shell thickness of 90 nm were prepared via a biomolecule (L-asparagine)-assisted hydrothermal route. N2 adsorption/desorption results revealed that the shells of the hollow microspheres were mesoporous structures.